solar heated water as inflow to the geaser

Please help, my plumber says, there should be seperate pipes for geaser and solar heated water in the bathroom. However, I think that solar heated water should flow into geaser where it could be further heated if required. Please suggest on this.

Problem is that we are facing difficulty in choosing well-trained plumber to diagnose leakage of our bathtub. We did many efforts changes whole sanitary bought expensive tub but a team of cheap essay help online haven't satisfied yet and still approaching an expert to handle this problem professionally.